During the laundering operation of fabrics it is highly desirable to provide the fabric, particularly man-made fabrics produced from synthetic fibres, with soil release properties.
Due to the hydrophobic nature of fabrics composed of partially or completely synthetic fibres, the removal of greasy soils and stains therefrom is particularly difficult. In order to address this problem, soil release polymers may be incorporated into the detergent composition. During laundering the soil release agents are adsorbed onto the surface fabric, thereby inducing greater hydrophobicity to the fabric surface. Once the fabric is treated with a soil release agent, the ease of removal of greasy soil and stains from the surface of the fabric is considerably improved.
The main types of soil release agents incorporated into detergent compositions, which provide benefits to primarily hydrophobic synthetic fabrics include synthetic soil release agents, preferably terephthalate based and polysaccharide ethers. Polymeric soil release agents are described in the art, for example U.S. Pat. No. 4,795,584 and EPO-253 567 disclose soil release polymers comprising ethyleneoxy terephthalate and polyethyleneoxy terephthalate units having a molecular weight of 900 to 9000.
Polysaccharide ethers such as cellulose ethers have been described for example in EPO 054 325 which discloses a detergent composition having reduced soil redeposition effects comprising carboxymethyl cellulose, a linear polycarboxylate and a cellulose either having a degree of substitution (ds) of at least 0.5 and a degree of polymerisation (dp) of less than 300. GB 1 534 641 discloses nonionic surfactant detergent compositions comprising cellulose ether soil release agents such as alkyl and hydroxyalkyl cellulose ethers. U.S. Pat. No. 4,441,881 discloses detergent compositions comprising modified cellulose ethers such as alkyl and hydroxyalkyl cellulose ethers having a molecular weight of 19000 to 185000 and a degree of substitution up to 3.
The soil release performance of the polysaccharide ethers may be substantially improved upon greasy/oily stains by increasing the amount of ether used or by increasing the molecular weight or degree of polymerisation of the ether. However, such higher molecular weight polysaccharide ethers are known to have detrimental effects on the clay soil removal and anti-redeposition performance of the detergent composition in which they are incorporated. This is particularly evident on fabrics after a number of repeated washing cycles or when high dosage or concentrations of detergent composition are utilised to clean heavily soiled fabrics. This problem is also acute on fabrics which contain a high percentage of synthetic fibres.
Synthetic soil release agents, particularly those soil release agents having a significantly lower molecular weight than the polysaccharide ethers have been used to address this problem. The clay soil removal performance of the detergent composition is not as detrimentally affected by the use of synthetic soil release agents in comparison with compositions comprising polysaccharide ether. Thus, synthetic soil release agents tend to be preferred. In particular those having a low molecular weight are preferred for solubility requirements and ease of manufacture.
Thus, it is an aim of the present invention to provide a detergent composition providing increased soil removal performance without negatively affecting the particulate/clay soil removal performance.
It has now been determined that this aim can be achieved by the use of the combination of a synthetic soil release agent having a molecular weight of less than 10000 with a nonionic polysaccharide ether having an average degree of polymerisation of 100 or more.
An additional advantage of the present invention is that this combination of synthetic soil release agent and polysaccharide ether provides improved overall cleaning performance, particularly on greasy food soils, mechanical oil stains and clay.
A further advantage of the present invention is that the improved cleaning performance, especially of clay soil is achieved on a broad range of fabric types, such as synthetics for example polyester and additionally on natural/synthetic blend fabrics such as polycottons.
Synthetic soil release agents and polysaccharide ethers have been described for example in U.S. Pat. No. 4,740,326 which discloses a laundry product comprising a substrate material coated with a soil release polymer for example dryer added sheets. The soil release polymers are selected from i) alkyl or hydroxyalkyl cellulose ethers having a molar degree of substitution (ds) of from 1.5 to 2.7 and average molecular weight of from 2000 to 100000 or ii) various ethylene terephthalate and polyethylene oxide terephthalate polymers having an average molecular weight of from 1000 to 100000 and mixtures of i) and ii).
U.S. Pat. No. 4,770,666 discloses laundry detergent compositions comprising peroxyacid bleach and soil release polymers. The soil release polymers are selected from i) alkyl or hydroxyalkyl cellulose ethers having a ds of 1.5 to 2.7 and an average molar weight of 2000 to 100000 and ii) various ethylene terephthalate and polyethylene oxide terephthalate polymers having an average molecular weight of from 1000 to 100000 and mixtures of i) and ii). However, the art does not suggest the synergic effect of the combination of synthetic soil release agents with polysaccharide ethers.